Vulcanization of rubber normally gives sulfidic cross-links in allylic position with respect to a double bond in the vulcanizate coupled with some cyclization instead of cross-linking as well as other undesirable side reactions. When elemental sulfur is the vulcanizing agent the cross-links are mainly polysulfidic and it is now recognized that polysulfidic cross-links as compared to monosulfidic cross-links reduce thermal stability of the vulcanizate. There have been suggestions to modify the cross-linking reaction by reacting rubber with dithiols to introduce an organic bridging element into the cross-link. However, dithiols add across double bonds of adjacent rubber molecules reducing unsaturation by a cross-linking reaction different from the classical vulcanization reaction. J. LeBras, Kautschuk U. Gummi, V15, WT 407-WT 418 (1962), FIG. 14; G. E. Meyer et al., Rubber World, V136, 529 (1957); C. M. Hull, Ind. & Eng. Chem., V40, 513 (1948). If a derivative of mercaptobenzothiazole is used as the accelerator in the classical vulcanization reaction with elemental sulfur it is known that mercaptobenzothiazole is generated in the process. Some theories devised to explain the mechanism of cross-linking rubber by the action of elemental sulfur and organic accelerator which is a mercaptan or derivative thereof assume that the accelerator reacts with sulfur to form polysulfide (herein meaning two or more sulfur atoms) and propose a cross-linking scheme involving free radical intermediates whereby a rubber polythiyl radical cross-link precursor forms which reacts preferentially with the polysulfide until all is combined with the rubber, then cross link formation begins. Coran, Rubber Chem. Technol. 37, 689 (1964). The theory is capable of explaining observed kinetics of vulcanization but it is difficult to write satisfactory steps for the actual cross-linking process itself. In vulcanization of diene rubber with tetramethylthiuram disulfide, evidence for formation of a rubber bound intermediate ##EQU1## which is the precursor to sulfur cross-linking, has been reported. Porter, The Chemistry of Sulfides, Interscience Publishers, p. 165-183. The mechanism by which a rubber bound intermediate forms is unknown. However, it is generally accepted that the initial step in sulfur vulcanization is the reaction of sulfur with a species derived from the accelerator.